Field
The present disclosure relates generally to thermal management of electronic devices and systems, and more particularly, to thermal management of wearable devices.
Background
Wearable devices, also known as wearable computers, are miniature electronic devices that can be worn by a person. An example of a wearable device is a smart watch, which is a computerized wristwatch with functionality that is enhanced beyond timekeeping. A smart watch may include features such as a camera, accelerometer, thermometer, altimeter, barometer, compass, chronograph, calculator, cell phone, touch screen, Global Positioning System (GPS) navigation, map display, graphical display, speaker, scheduler, watch, mass storage device, and rechargeable battery. It may communicate with a wireless headset, heads-up display, insulin pump, microphone, modem, or other devices.
Because of the increasing number of functionalities and improving computing power of wearable devices, an increased level of heat is emitted by these devices while performing functions. Therefore, improved thermal management of wearable devices is desirable.
One of the most important temperature specifications in mobile devices is skin temperature or surface temperature. The skin or surface temperature corresponds to the temperature at the outside surface of a mobile device. Temperatures at one or more surfaces of mobile devices may become too hot to touch, thus leading to uncomfortable user experience. Therefore, the skin or surface temperature needs to be low at the outer surfaces where the user is touching the device. For many typical mobile device usages, the upper limit of acceptable skin or surface temperature may be reached before electronic components, e.g., integrated circuits (IC), power sources, etc., within the mobile device reach their junction temperature. The junction temperature is the highest operating temperature of the electronic components. When the upper limit of acceptable skin or surface temperature is reached before electronic components within the mobile device reach their junction temperature, the mobile device goes to thermal mitigation in order to reduce heat emission and lower the skin or surface temperature. Thermal mitigation may include reducing clock speed or shutting down one or more electronic components of the device from time to time. Thus, the performance of the mobile device will be limited because of the thermal mitigation, while the operating temperature of the electronic components is still well below the junction temperature. This prevents the mobile device from reaching its maximum operating capabilities. The skin or surface temperature issue can be more severe in wearable devices as wearable device are smaller and directly in contact with user's body (e.g., wrist).